Many network applications can benefit from the knowledge of network capacity of an end-to-end network path. Network capacity is referred to as the transmission rate of the slowest link of a set of network links, forming a network path from a source to a destination. It is often one of the metrics required in the diagnostic services for network performance. Due to the proliferations of ADSL, DOCSIS cable networks, VSAT, and others, the downstream data rate (Cdn) and the upstream data rate (Cup) of a round-trip network path are usually different. For example, the Cup and Cdn for the existing xDSL technologies are determined by many factors, such as the wire quality, transmission distance and different broadband offerings, and the data rates span a wide range. Therefore, a forward path that traverses from a source to a destination and a reverse path that traverses from the destination back to the source can possess different network capacities.
Measuring network paths with asymmetric capacities is a challenging problem. Forward capacity of a network path from a measuring node to a remote node, reverse capacity of a network path from the remote node to the measuring node, faster-path capacity (maximum of the forward capacity and reverse capacity), and slower-path capacity (minimum of the forward capacity and reverse capacity) are collectively known as asymmetric capacities. A possible approach to measuring the four types of asymmetric capacities is to perform two one-way measurements on the forward and reverse directions. However, many existing one-way measurement tools, such as pathrate proposed in C. Dovrolis, P. Ramanathan, and D. Moore, “Packet dispersion techniques and a capacity-estimation methodology,” IEEE/ACM Trans. Netw., 12(6), 2004, require controlling both nodes of a path, thus making this approach impractical for measurement with arbitrary remote nodes. On the other hand, only few tools—DSLprobe proposed in D. Croce, T. En-Najjary, G. Urvoy-Keller, and E. Biersack, “Capacity estimation of ADSL links,” Proc. ACM CoNEXT, 2008 and SProbe proposed in S. Saroiu, P. Gummadi, and S. Gribble, “SProbe: A fast technique for measuring bottleneck bandwidth in uncooperative environments,” Proc. IEEE INFOCOM, 2002 based on packet-dispersion methods, and the flooding-based method proposed in M. Dischinger, A. Haeberlen, K. Gummadi, and S. Saroiu, “Characterizing residential broadband networks,” Proc. ACM/USENIX IMC, 2007—can be used for measuring asymmetric capacities without installing additional software at the remote node, but their utility is limited by the restrictions on packet size.
All existing tools for measuring asymmetric capacities (AsymProbe proposed in L. Chen, T. Sun, G. Yang, M. Sanadidi, and M. Gerla, “End-to-end asymmetric link capacity estimation,” Proc. IFIP Networking, 2005, DSLprobe, SProbe, and the flooding-based method) generally require setting probe packets much larger than response packets to measure the forward capacity, and setting probe packets much smaller than response packets to measure the reverse capacity. Such requirement introduces two serious limitations. First, they cannot measure all degrees of capacity asymmetry, because the packet size is upper bounded by the path Maximum Transmission Unit (MTU). Second, they generally cannot support all measurement scenarios, because they may not be able to elicit response packets of the required size from the remote node. For example, DSLprobe elicits only small TCP Reset (RST) packets (but not large response packets) from remote residential broadband users. Moreover, compared with the packet-dispersion method, the flooding-based method performs the measurement by sending high-rate packet trains to saturate the bottleneck link, and the packet rate limits the maximum capacity it can measure.
As a result, the need remains for a reliable method in communication networks which obtains the four asymmetric capacities accurately, rapidly and efficiently without the asymmetric packet sizes requirement or overwhelming the bottleneck link.